Atom probe field ion microscope and levitation studies of the decomposition and crystallization of undercooled Zr-Ti-Cu-Ni-Be melts

Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glasses were prepared by cooling the melt with a rate of approximately 10 K/s. Atom probe field ion microscopy investigations on these samples reveal that the alloy decomposes in the undercooled liquid state into two undercooled liquid phases with different Zr and Be concentration. For the used cooling rate the size of the phases separated domains is of the order of 50 nm. The decomposition was monitored in undercooling experiments of levitated samples as well. The cooling curves show the decomposition as a weak recalesence effect and indicate that the miscibility gap between the two undercooled liquid phases opens up below about 800 K. The decomposition is followed by two crystallization events. The results are compared with TEM and DSC investigation suggesting that the decomposition in the undercooled liquid state triggers the crystallization and is a contributing factor to the extremely high glass forming ability of the alloy.